340

THE PRODUCTION OF SULPHUR DIOXIDE

process introduced by him at Briton Ferry, near Swansea.
The copper-matte produced there could not be roasted in
Mansfeld kilns, nor in ordinary pyrites-burners. The desired
result was obtained by increasing the heat, in the first instance
by a suitable treatment of the matte, and in addition to this
by improving the construction of the burners. The matte was
rendered porous by tapping it on to a sand-bed slightly
moistened and dusted over with fine coal. It was then
crushed by a Blake's stone-breaker, in which one of the
corrugated faces had been substituted by a smooth one, so
that flat, more tightly lying pieces were obtained, which were
separated from the smalls by a riddle with openings of f in.
width. The burners were of the ordinary shape of English
pyrites-burners, described above, but of slightly different
dimensions :—Grate-surface 4 ft. 3 in. by 4 ft. 4 in.; area at
the level of the upper working-surface 5 ft. by 4 ft. 9 in. ; height
from grate-bars to the upper working-surface 2 ft, to spring
of the arch 3 ft. 4 in., to the crown of the arch 3 ft 8 in.;
smoke-flue at the lowest point 6 in,, at the highest I ft. 4 in. ;
total outside height 7 feet 10 in. The heating-up takes place
from the top, exactly as described in the text ; the burners
are ready for work in two or three days. Each burner then
receives a charge of from 6 to T\ cwt. of crude matte every
twelve hours. The draught must be well regulated; there
should be a slight plus-pressure within the burner. In this
way mattes containing from 20 to 47 per cent copper are
treated. The poorer matte yields rather hotter and better gas
and more sulphuric acid than the richer. With 20 per cent,
matte the roasted product contains 9 per cent, sulphur, with
rich matte it contains 11 per cent sulphur ; both are at once
ready for the concentrating work. From 40 per cent matte
about 47 or 48 per cent of the weight of roasted matte is
obtained in the shape of chamber-acid of 11 o° Tw,, with con-
sumption of 0*8 to i-o nitre per cent of chamber-acid. The
gases are hot enough to thoroughly decompose the mixture of
nitre and sulphuric acid in the nitre-oven and to denitrate the
acid in the Glover tower; the acid flows from this with a
temperature of 140° to 155°.